Multiple Fault Codes

I have begun to have multiple fault codes on my 2001 Boxster S with 107,000 miles on it. I have cleared them twice and cleaned the MAF (which was replaced at 63,000 miles) but they keep showing up plus when the check engine light comes on the car runs about 10-15 degrees hotter.

Could be bad coils. I drove 317K miles with no coil failures but not everyone will have the same luck. You'll have to check the coils for any signs of cracking. If you find a coil with any signs of cracking replace all coils. If due or nearly due on time/miles might as well replace the spark plugs "while you are there".

Be sure you use the right plugs. Check the gaps. Be sure you install the plugs correctly (no anti-seize), torque the plugs (use a torque wrench), and make sure the coil/plug connection is good and the coil to wiring harness electrical connection is good.

I note the misfires are confined cylinders 4 and 6. Misfires limited to one bank signal a problem with the affected bank. With one exception. In at least one case a bad MAF had the cylinders of one bank misfiring while the other bank's cylinders were not misfiring. There can be another possible explanation for a "bad bank". I'll cover this below.

Based on my experience let me cover some other possible explanations...

107K miles... Is the AOS original?

Another source of mixture related error codes can be a leaking oil filler tube cap. Check this with the engine running at hot idle. See if when you move the car you cause a vacuum leak. If you can the cap should be replaced.

Is the MAF at fault here? I had a MAF go bad but I can't recall the error codes now. There is the shade tree mechanic's MAF test. Disconnect the MAF at the wiring harness. Clear the error codes. Road test the car. If the error codes come back the MAF is not the problem. If the codes do not come back reconnect the MAF, clear the error codes again (to reset the learned fuel trims to their defaults) and road test the car. If the codes come back that's a good sign the MAF is bad.

Be aware with the MAF disconnected it is possible the CEL will come on but the error will be due to the MAF being disconnected. But the misfires/P1128/P1130 error codes are the ones of interest.

However with the engine temperature going up concurrently with the CEL/error codes I'm not real comfortable with the engine being run any more than absolutely necessary. I generally add that this should be under the supervision of a Porsche tech as he goes about diagnosing the cause of the codes.

More on problem confined to one bank... There can be a problem with the VarioCam solenoid/actuator. If either of these act up the camshaft timing will not be right and the DME will recognize a problem from the O2 sensor readings from the bank with the suspected bad solenoid/actuator. The DME will adjust fueling to try to get the O2 readings it expects and in adjusting the fueling can go too far and the engine, at least some of the cylinders of the affected bank, will misfire.

When my Boxster's passenger side VarioCam solenoid/actuator failed there were no active error codes but there was on pending code that pointed to the VarioCam solenoid/actuator. I don't recall the error code now.

The AOS was replaced about four years ago at 89,000 miles. It sounds like I will print out all of the suggestions here and take it to my mechanic. If he is not comfortable I will need to take it a couple of hours away to the dealer.

My mechanic got back to me today and he wanted to start with the spark plugs (I replaced them on schedule a few years ago and will likely have him do it as I am not that ambitious anymore!) and then move the coils around to isolate the problem before replacing them.

The problem is very unlikely to be the spark plugs, especially given that they were replaced relatively recently. I believe the service interval on 2001 plugs is 60k miles. And even then they degrade gracefully and don't start misfiring at 60k miles. I think it's just a waste of money to replace them. If you're really concerned you can pull one of the plugs that is throwing a code and inspect it. My guess is that it will look just fine.

Swapping the coils is a good diagnostic step but is probably not necessary. Almost always, coils that fail even when it's not raining have obvious visual flaws, such as cracks.

The other possibility is that the plugs on those two coils aren't seated properly. If that's the problem, swapping them may make the problem go away and lead you to the wrong conclusion.

My mechanic got back to me today and he wanted to start with the spark plugs (I replaced them on schedule a few years ago and will likely have him do it as I am not that ambitious anymore!) and then move the coils around to isolate the problem before replacing them.

Neil

Generally I don't like to go against what a professional mechanic advises. He's the pro. I'm not.

I will say replacing the plugs is not what I would start with I think. I've run plugs 60K miles in my Boxster and after having them replaced did not notice any change (good or bad) from the engine. I've run the plugs in my Turbo to the mileage at which the factory called for the plugs to be replaced and the Turbo engine never showed it cared one way or the other. Kind of disappointing in a way to go to the trouble/expense of replacing the plugs only to have the engine fail to show its appreciation. (OTOH, the idea is to replace these components at some point *before* they cause the engine to be affected.)

But replacing the plugs is a starting point.

You shouldn't need to mention this but be sure he carefully checks the coils for any signs of cracks. If he finds one with any cracks my advice would be to replace them all. I never replaced the coils in my Boxster, even at 317K miles -- though I had planned on this had I gotten that pesky P1128 error code addressed -- but when I replaced the coils at around 140K miles on my Turbo the engine perked up some. Even though the engine was not misfiring the coils had deteriorated to the the point the engine was affected. But it took new coils to make this evident.

In both the case of my Boxster and Turbo replacing the O2 sensors made a positive difference in how the engine ran. But in both cases both cars are manifesting O2 related error code.

I'm not really a fan of moving coils around. The less handling these receive, and this includes the wiring both at the coils and the wiring harness connectors to which the coils must be properly connected, the better. The Porsche techs treated the coils like glass handling them with care.

The problem is the coils are moved around. If the misfires follow the coils then all the coils should be replaced. If the coils are suspected of being the problem they should just be replaced. This at least saves the labor of gaining access to the coils twice. And labor is the biggest expense of coil replacement.

While my Boxster coils lasted a long long time -- 16 years, 317K miles -- I know from my reading posts on the UK Porsche forums cars driven in areas where there is more humidity, more rain fall, coils can and do fail much sooner, even under 100K miles.

Thanks for all the comments and suggestions posted here. I was out of state last week but had taken the Boxster into my mechanic while I was out of town. I shared all the comments here. Bottom line: they found the same codes I had and finally found it was an intake vacuum leak. The leaking hose was reattached and tested and everything works perfectly. It was a little pricey at well over $300 for labor only, no parts needed but the car runs perfectly and I was expecting a bill many multiples of that expense.